I had a look at Cannon/Lowe connections.
Margaret Ouchterlony Lowe (1780-1850) married the Reverend David Cannan (1774-1854) in Brechin in 1804. He was minister of Kirriemuir, then Murroes, then Mains and Strathmartine. There were 11 children including Thomas, born 1817.
Thomas was a planter in Mysore. He made a will in 1859, leaving legacies to his cousins, Helen Jane, William Alexander and George James Campbell, three of the five children of William Patrick Allardice, whom he appointed an Executor along with William Campbell Onslow, whose son Harrington later married Helen Jane Allardice.
He also left legacies to David and Margaret Forgan, 'commonly known as Cannan', the children of his late sister Helen Cannan (1812/3- 1845) from her marriage to James Forgan (1806/11- 1852), and to the children of his brother Alexander Cannan, Captain in the Madras Army.
James Forgan appears to have blotted his copybook. He was tried at the spring circuit in Perth (that's the original Perth, not its namesake Perth, Western Australia) on 26 April 1852 on charges of theft, habit and repute, and previous conviction. He died in Dundee Prison about three weeks later and was buried in the Howff, Dundee on 22 May 1852. There are court papers in the National Records of Scotland but I have not seen these.
So yes, Margaret Ouchterlony Lowe was the sister of Catherine Lowe. Their parents were Joseph Low(e) and Margaret Young.
Wouldn't it be interesting to know why he left nothing to his cousin John McDermid Allardice, brother of the three cousins to whom he did leave legacies? And why he passed over all the rest of his 10 siblings and their families?